Degree of Corridor SegregationIntroduction IntroductionDegree of segregation refers to the amount of interaction permitted between rail vehicles and pedestrians, cyclists and general traffic. This can range from fully-segregated rights-of-way (meaning no interaction with other modes) to un-segregated rights-of-way (meaning that the rail vehicles operate on-street in traffic lanes shared with general traffic). From a technology standpoint, the degree of segregation impacts the design and operating characteristics of the rapid transit network, affecting major issues such as system safety, capacity and speed. Key issues to consider include:
It is noteworthy that decisions to be made regarding degree of segregation impact not only the vehicle operating characteristics and issues identified above, but also public access to and across rapid transit corridors. This in turn prompts discussion as to the aesthetics of the rapid transit network (particularly fully-segregated rights-of-way) and how they integrate into their surroundings. Intersection design and safety where partially-segregated rights-of-way interact with other travel modes will also require careful consideration. Ottawa’s approved rapid transit network consists of three major types of corridor (Primary, Transit Intensive and Transit Priority). Within these three corridor types, a variety of operating conditions may be encountered, each of which has different requirements which will influence the degree of segregation provided. The unique corridor segments identified in the TMP rapid transit network are:
Figure 1 illustrates where the different corridor types are located on the rapid transit network. It is noteworthy that while the degree of segregation is self-evident for some corridor segments (i.e. tunnel segments will be fully-segregated), while other corridor segments such as the Greenbelt will need to be studied in further detail in order to determine the degree of segregation to be provided in these areas.
Figure 1: Corridor Segment Characteristics of the Rapid Transit Network Right-of-way OverviewThe following provides an overview of the characteristics associated with different degrees of segregation. Depending on specific constraints associated with some technology options, the degree of segregation can vary along a corridor depending on the routing options and right-of-way width available. Some technology decisions restrict the degree of segregation which can be provided from other modes due to operational and safety concerns.
Fully-segregatedIn a fully-segregated right-of-way rail vehicles travel in an exclusive corridor separate from other travel modes, with no interaction permitted between modes. This can allow for greater system speed and capacity as the movement of rail vehicles is not restricted by other travel modes. The rail corridor may be underground, at-grade or elevated for all or part of its length. The subway systems in Montreal and Toronto and Skytrain system in Vancouver are good examples of fully-segregated rights-of-way. Parts of the LRT systems in Edmonton and Calgary also run along fully-segregated rights-of-way. Fully-segregated rights-of-way require wider corridors (more property), to accommodate security fencing, grade-separations at cross streets, signalling, power supply requirements and parallel pedestrian and cycling facilities which may be provided within the corridor. Design standards are employed to maximize speed where possible (e.g. larger curve radii and gentler grades). Station facilities are generally more extensive to accommodate larger passenger flows and facilities such as bus transfer platforms. Stations are typically spaced further apart due to balance cost, and the desire to achieve a higher operating speed. Movement of rail vehicles is typically governed by advanced signalling systems due to the greater speeds involved. Long trains can be accommodated to increase the capacity of the line, and automatic train operation is possible as there is little risk of intrusion into the travel corridor. Partially-segregatedIn a partially-segregated right-of-way rail vehicles travel in an at-grade corridor which may be shared with a road, utilities or other land uses. When using a road corridor, the transit right-of-way consists of exclusive lanes separated from general traffic by bollards, curbs or pavement markings. These may be located in the median, on one side or in the curb lanes of a roadway. Where the right-of-way is not within a road corridor, level crossings may be provided which allow pedestrian, cyclists and general traffic to cross the corridor. Rights-of-way are narrower than with fully segregated corridors and can generally fit within existing suburban road corridors, or be integrated with other land uses. Station facilities are less extensive and more closely spaced than in fully-segregated rights-of-way in order to support adjacent development along an urban road corridor. Operating speeds are typically lower due to the interaction with other vehicles, pedestrians and cyclists, and service reliability may be impacted by conflicts with other modes. Movement of rail vehicles may be governed by line of sight and traffic signals at intersections/crossings, as well as more advanced signalling systems to maintain train separation. Transit signal priority is generally provided in order to reduce delay to transit vehicles. Individual vehicles can be coupled to operate as trains to increase the capacity of the line but train length may be limited by intersection and spacing, and the larger station facilities needed to accommodate longer trains and passenger crowds. Automatic train operation is not possible due to interaction with other travel modes along the corridor. Un-segregatedIn un-segregated rights-of-way, rail vehicles travel along existing road corridors in shared lanes with general traffic. No additional right-of-way is required to accommodate the transit corridor. The streetcar system in Toronto would be a good example of an un-segregated right-of-way. Station facilities are basic, with passengers typically waiting at the curb and entering the roadway to board the rail vehicles. Operating speed and service reliability is governed heavily by prevailing traffic conditions. Movement of rail vehicles is by line of sight and intersection traffic signals only, with transit signal priority provided to reduce delay to transit vehicles. The ability to increase capacity of the line by coupling individual vehicles into trains is restricted by the ability to operate safely in mixed traffic, intersection spacing and lack of dedicated station facilities. Automatic train operation is not possible due to interaction with other travel modes along the corridor. As touched upon, the degree of segregation provided will have impacts on other technology decisions, primarily signalling, power collection, automatic train operation and multi-vehicle fleet options. SignallingFully-segregated rights of way allow for faster speeds, better driver viewing and increased passenger safety. As such signalling sections can be optimised for vehicle performance and provide a better selection of opportunities of using a number of signalling and operational techniques. Partial segregation introduces an element of risk from other transportation modes that can be associated from unplanned failure conditions or catastrophic events such as vehicle collisions, road vehicles failing to adhere to traffic lights and vehicles mounting the median barrier. Partial segregation allows the use of a number of signalling techniques which will vary depending on the degree of segregation along the corridor (i.e. inter-action between transit vehicles and other modes limited to level crossings of the corridor versus running in the median of an arterial road). Where partially-segregated rights-of-way are located within a road corridor, transit priority signalling is used to reduce delay to transit vehicles. Un-segregated rights of way introduce the biggest hazard to a rail system as they introduce vehicular events and human events that must be considered. Signalling systems cannot pre-empt or control human behaviour and the risks associated with accidental or intentional intrusion on the line. As un-segregated rights of way require human intervention it is common for this right of way to use line of sight operations accompanied with some basic signalling to maintain vehicle headways, and transit priority signalling used to reduce delay to transit vehicles. Power CollectionFully-segregated rights of way allow greater flexibility in the use of different power collections systems as the exposure to passengers is minimised. Third rail power collection is only used in fully-segregated rights-of-way due to the risk of accidental contact by other corridor users. Partially or un-segregated rights-of-way allow a degree of isolation, however fences and barriers may be required to reduce the possibility of access to the power systems. Overhead catenary is the preferred method of reducing the possibility of passengers being exposed to live conductors although the network design should pay particular attention to catenary areas supported underneath bridges and high positions where the public may be able to gain access or drop items onto the overhead lines. Some alternative power collection systems such as APS or IPT have been developed to deal with the dual issues of aesthetics and isolation of power supply. Automatic Train OperationFully-segregated rights-of-way allow the greatest flexibility in terms of vehicle operation as ATO can be considered due to the reduced risk of intrusion into the right-of-way. Complex systems to monitor possible intrusion are employed and linked to the signalling and control systems of the network to ensure intrusion does not result in collision. Both driver-controlled and fully automatic operations can be supported. Partially and un-segregated rights-of-way do not generally support ATO operation is this not used where there is any potential human interaction or interface between the rapid transit vehicles and other modes of travel. Single versus multi-vehicle FleetWhile rail vehicles that can operate in fully, partially and un-segregated rights-of-way are available, given the restrictions which partially and un-segregated rights-of-way impose on other technology decisions (e.g. signalling, power collection) discussion as to whether a fleet of consisting of a single vehicle-type (possibly incorporating multiple technologies) which can operate over the entire network, or a fleet consisting of multiple vehicle-types which may be restricted to specific corridors in the rapid transit network, should be acquired. This issue is explored further in the single versus multi-vehicle fleet section of this report. As outlined above, it is generally found that as the degree of separation employed becomes more restrictive (i.e. increasing in segregation), the flexibility to employ different technology options increases. If a single vehicle-type is pursued, the least restrictive right-of-way in the rapid transit network will therefore govern technology decisions with respect to signalling, power collection and automatic train operation. Acquisition of a single vehicle-type which can accommodate multiple technologies (e.g. third rail and overhead power collection) to address this issue can be pursued but will likely increase costs and risks involved in fleet development. ConclusionsThe degree of segregation provided along the rapid transit network will impact the design and operating characteristics of the rapid transit network. Additionally, degree of segregation impacts not only vehicle operating characteristics, but also public access to and across the rapid transit corridors. This in turn prompts discussion as to the aesthetics of the rapid transit network (particularly fully-segregated rights-of-way) and how they integrate into their surroundings. Vehicles are available which can operate on fully, partially and un-segregated rights-of-way, however some vehicle technology choices (e.g. signalling, power collection, automatic train operation) may require more restrictive rights-of-way in order to reduce or eliminate the potential for intrusion or interaction with other travel modes. It is generally found that as the degree of separation employed becomes more restrictive (i.e. increasing in segregation) the flexibility to employ different technology options increases. |
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